The invention relates to antivibration devices intended to be interposed for support and shock-absorbing purposes between two rigid elements, the shock-absorbing bringing into play the driving of a liquid through a restricted passage, and the movements relating to damping the two rigid elements comprising on the one hand, oscillations of relatively large amplitude (that is to say, greater than a millimeter) at a relatively low frequency (that is to say, less than 20 Hz) and on the other hand, vibrations of relatively small amplitude (that is to say, less than 0.5 mm) at a relatively high frequency (that is to say higher than 20 Hz).
As a non-limiting example, it is indicated that such supports can be mounted between a vehicle frame and the engine of this vehicle, the relatively ample oscillations to be damped, being those created by the irregularities and variations in dip of the ground during the travel of the vehicle over this ground, and the vibrations to be damped, being those due to the operation of the engine.
The invention relates more particularly, among supports of the type concerned, to those which are constituted by a fluid-tight box, interposed between the two rigid elements, the said box comprising two rigid parts which can be made fast respectively with the two rigid elements, a first elastic wall connecting in fluid-tight manner one of the two rigid parts to a rigid annular armature forming a portion of the second part, this first wall bounding with the first part one of the two axial ends of the box and ensuring the role of support between the two parts, for which it offers good resistance to axial compression, a second elastic wall, borne in fluid-tight manner by the annular armature and bounding the second axial end of the box, a deformable partition also borne in fluid tight manner by the annular armature, between the two elastic walls, and dividing the inside of the box into two chambers, namely an operating chamber comprised between the partition and the first elastic wall, and a compensating chamber comprised between the partition and the second elastic wall, these two chambers communicating with one another through the above-said restricted passage, means for limiting to a small amplitude, that is to say less than 1 mm, the deformations of the partition in the axial direction perpendicular to its middle plane, and a liquid mass filling the two chambers as well as the restricted passage.
With such a support, a vibration of high frequency and of low amplitude exerted between the two rigid elements generates corresponding relative movements of the two rigid parts, which are transmitted to the deformable partition by the liquid contained in the operating chamber, and are manifested by a rapid succession of alternate deformations of this partition perpendicular to itself, of amplitude lower than the maximum possible value: the dimensions of the partition are selected to be sufficient, so that the latter can thus absorb the signaled movements without the liquid being driven through the restricted passage in opposite directions in synchronism with the vibration.
On the other hand, for oscillations of higher amplitude and of lower frequency, the amplitude of the corresponding deformations of the partition reaches its maximum possible value and the liquid is then driven through the restricted passage, which ensures the hydraulic damping of this liquid through its throttling in this passage.
With current modes of construction of supports of the type concerned, the mass supported (engine or the like) is only connected to the bearing structure (frame of the vehicle) by the first elastic walls of the supports.
It can therefore happen that certain abnormally high stresses exerted on the supported mass, such as those due to sudden decelerations or accelerations, are manifested by excessive deformations of these walls which can result in their tearing away or their rupture and generate shocks producing damage between said supported mass and its immediate environment.